1. Field
Example embodiments relate to light-sensing apparatuses, methods of driving the light-sensing apparatuses, and optical touch screen apparatuses including the light-sensing apparatuses.
2. Description of the Related Art
A touch screen apparatus is an apparatus for directly receiving input data from a display screen that executes particular software functions by sensing locations of the display screen touched by a hand or a stylus of a user. Generally, a touch screen apparatus is formed by adding a touch panel to a common display panel. Examples of touch panels include resistance film touch panel, electrostatic capacitance touch panel, surface acoustic wave (SAW) touch panel, infrared ray touch panel, piezoelectric touch panel, etc. Recently, such touch screen apparatuses are widely used in various fields as input devices replacing keyboards or mice.
A general touch screen apparatus requires a direct touch on a display screen by a hand or a pen. However, as the size of display apparatus increases, if a distance between a user and a display device increases, it may be difficult to apply such a direct touch. Therefore, an optical touch screen apparatus which may perform the same functions as conventional touch screen apparatuses by sensing light instead of touch by a hand or a pen has been suggested. An optical touch screen apparatus is expected to be useful not only for communication between a user and an apparatus, but also for communication between users.
To embody an optical touch screen apparatus, fine-sized light-sensing devices for sensing light are demanded. An example of generally used light-sensing devices includes an amorphous silicon thin-film transistor (a-Si TFT). However, in a case of an a-Si TFT, the change in current due to light is insufficiently large. Therefore, charges generated by a photodiode during the application of light are accumulated in a capacitor for a predetermined period of time and a signal related to light intensity is generated based on the amount of charges accumulated in the capacitor. In this case, sensing time may be delayed as much as a period of time for accumulating charges in the capacitor, and parasitic capacitance may increase as the size of an optical touch screen apparatus increases.